Quiz 20

A 38 year old lady sees you in your office because of progressive shortness of breath. She has been a smoker for 18 years, smoking half a pack of cigarettes a day. You order a set of PFTs on her. She is due to see a pulmonologist but gets progressively short of breath. She goes to the ER. Her ABG shows pO2 of 53, pCO2 of 50. pH is 7.30. She is breathing at a rate of 32 a minute. She gets intubated and the respiratory therapist calls you to tell you of a sudden worsening of her breathing.

Q1. Out of all of the following findings, which will least suggest tension pneumothorax (least specific)?
  1. High Peak pressures
  2. High plateau pressures
  3. Low exhaled tidal volume
  4. Pulsus paradoxus

Answer is choice 1(High Peak pressures).  It (High Peak pressures) is the least specific of all the above and is most commonly due to secretions in the airway. High plateau pressures will be present when the chest wall expansion is difficult but is not due to airway narrowing. The difference in the plateau and the peak is an indicator of the airway resistance being faced. Peak pressure - just as the name indicates is the highest pressure recorded - and is always higher than the plateau.

Low exhaled tidal volume means that there is less air coming out of the person compared to what went into the persons lungs. It is measured by ventilators at their attachment to the corrugated tube that we use to connect the vent to the Endotracheal tube. This means that if there is a leak at a point beyond this (for instance in the tube or at the endotracheal cuff or into the chest wall - the last example being pneumothorax) then there will be less return compared to the inhaled air. This is not a common scenario - its commonest cause is leaks but beware of the pneumothorax and always rule this out first.

Pulsus paradoxus should be taken seriously and should be investigated. Pneumothorax is one of its few causes.

Q2. Which of the following will lead you to think of cardiac pulmonary edema?

  1. High peak and plateau pressures
  2. High plateau pressures but not peak pressure
  3. High peak pressures but not plateau pressure
  4. Low tidal volume inspite of being on Assist control mode ventilation
  5. High residual volume as measured by single breath method

The answer is choice 1 (High peak and plateau pressures). The second choice cannot exist because if plateau pressures are elevated, peak pressure too will be elevated. Choice 3 indicates increased airway resistance and not parenchymal or chest wall resistance. In pulmonary edema, plateau too will be elevated. Choice 4 again is usually impossible (from the internist's point of view) because the tidal volume is fixed in the Assist control mode. Choice 5 is an irrelevant choice in this question.